With the scaling down of semiconductor devices such as dynamic random access memory (DRAM), new materials with high dielectric constant are required. Indeed, in order to store a sufficient charge in a capacitor with a smaller surface area, capacitors with higher permittivity are needed. Among high-k dielectrics, Group 4 based materials, such as HfO2 or ZrO2, are very promising since their dielectric constant is higher than SiO2 or Al2O3. However, their dielectric constant varies depending on their crystalline form (Thin Solid Films 486 (2005) 125-128).                the cubic/tetragonal crystalline phase of the ZrO2 layer, which is the phase having the highest k-value, has also been stabilized by doping ZrO2 with a small amount of silicon or germanium (Journal of Applied Physics, 2009, 106, 024107; Applied Physics Letters, 2011, 99, 121909).        
Group 4 alkylamide precursors containing cyclopentadienyl ligand have been developed, such as the one show below (Dussarrat et al., WO2007/141059; Niinisto et al., Journal of Materials Chemistry (2008), 18(43), 5243-5247). These precursors show a higher thermal stability in comparison to the tetrakis alkylamide precursors.
wherein R1=H, Me, or Et; R2&R3=C1-C4 alkyl group.
Similar to these compounds, Group 4 precursors containing silylcyclopentadienyl ligand have been described in the literature as shown below:
wherein R=Cl, NMe2, OSiMe3, CH2SiMe3, C6H5 and CH2Ph (Journal of Organometallic Chemistry, 2004, 689, 1503 for Ti methoxy compounds, JP2005/171291 to Tosoh for Ti alkylamino compounds, KR2008/0101040 to UP Chemical Co. Ltd. and Journal of Organometallic Chemistry, 1997, 547, 287 for Zr compounds).
A need remains for developing liquid or low melting point (<50° C.), highly thermally stable, with low viscosity, Hafnium precursor molecules suitable for vapor phase thin film deposition with controlled thickness and composition at high temperature.